TM 5-811-7
(6) Compute the minimum weight of riser anode material needed (eq C-1):
YSI
W'
,
E
where Y = 10 years, S = 1.0 pound per ampere-year, I = 3.62 amperes, and E = 0.50.
(10 yr)(1.0 lb/A&yr)(3.62A)
W'
,
0.50
W = 72.4 lb.
(7) Find the main anode circle's radius using equation D-8:
r = (DN)/2(B + N)
(eq D-8)
where D = 56 feet and N = 10 (assumed number of anodes). Thus,
56 ft 10
r'
2(3.1416 % 10)
r = 560/26.28
r = 21.3 ft, use 22 ft.
(8) Determine the spacing for the main anodes. Generally, the distance from the anode to the tank wall
and tank bottom is about equal; this distance should be about one-half the circumference between anodes.
(a) To find circumferential spacing, use equation D-9:
C = (2 B r) / N
(eq D-9)
where r = 22 feet (anode circle radius) and N = 10 (assumed number of anodes). Thus,
2 3.1416 22 ft
C'
10
C = 13.8 ft, use 14 ft.
(b) The cord spacing is approximately the same as circumferential spacing; 14 feet will be used (fig
D-8).
D-15
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